The present invention relates to an electric motor driven vehicle and the power unit thereof, and particularly, to an electric motor driven vehicle and power unit thereof capable of being driven by a motor from starting and capable of operation at reduced load at low speed.
An electric motor driven vehicle, such as an electric motor driven bicycle with a rear wheel driven by a motor through a transmission mechanism is known, and for instance, is disclosed in Japanese Utility Model Publication Official Gazette No. Sho-48-14271. In the above referenced known electric motor driven bicycle, a chain wound between a driving sprocket and a pedal is capable of being driven by the pedal. The driving sprocket is also made to be possibly driven by a DC motor; the DC motor connected to a battery through a governor. In order to operate the electric motor driven bicycle, speed is raised by man power through operation of the pedals, and when the speed reaches a predetermined running speed, the governor switch turns ON and the DC motor is started so that motor driving of the vehicle can be started.
Generally, a motor has a peculiarity that torque and current are large in the case of a low rotational state and efficiency becomes decreased. Here, the efficiency is given by the following expression: EQU n=1.027.multidot.N.multidot.T/(I.multidot.V)
(N=number of rotations, T=torque, I=current, and V=voltage).
When a load is applied to the motor in such a low rotational condition, a negative effect occurs in that an amount of electric power consumption becomes larger and the cruising distance is shortened. Also, heat generation quantity becomes larger whereby deterioration of operational capacity soon results. The extent of good operational efficiency of the motor is therefore primarily limited to be within a relatively narrow range.
Therefore, although it is thought that the motor may not be started until it reaches a predetermined running speed as in the aforementioned example, it would be advantageous if motor driving and man power driving could be applied together in this case. Accordingly, such an electric motor driven vehicle is expected that can be driven by a motor from the start.
Further, there is also a need to adopt an integrally structured transmission mechanism with the motor to efficiently cool the motor because the heat generation quantity of the motor is great. Such a cooling system would result in a simplified wiring structure of the electric power supply cord of the motor.